Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, silicon, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates a prior art device described in more detail in US 2012/0012856. US 2012/0012856 describes shaping the sapphire substrate of a III-nitride light emitting diode. US 2012/0012856 describes the device of FIG. 1 in paragraph 45. The device of FIG. 1 is “a GaN light emitting diode [401] comprising a sapphire substrate 404 and an epitaxial layer 402. Slopes 405 and depressions 4042 are both formed” in the substrate. A “lower portion of the sapphire substrate 404 is enveloped in a distributed Bragg reflector 407. A layer of silver glue 408 is applied below the distributed Bragg reflector 407 and on slopes 405 of the sapphire substrate 404 for reflecting light from the slopes 405 of the sapphire substrate 404. As we can expect, the . . . [device of FIG. 1] has good light extraction efficiency due to increase of side light beams.”